1. Class V. In 15 miles, there are 18 named class V rapids, many of them are over 1/2 mile long. In between, there are a lot of class III and IV unnamed features. The wide angle lens on the camera really flattens out the river and doesn't give a very accurate portrayal of how big it is in there. But then again, camera's never do. Unless you're a stellar photographer. check out these photos from 2 years ago: Catarafting North Fork of the Payette River in Idaho, photos by Mike Reid, Idaho Whitewater. - All Outdoor Photography by Mike Reid, Boise Wedding and Outdoor Portrait Photographer
2. Not sure what you mean. There are several different runs in the payette river system that range from class II through V. The north fork from smiths ferry to banks (where that footage is from) is not run very often by rafts. There were two very very talented boaters there last weekend that R2'd top to bottom. I didn't see them, but I did see them last year. Very impressive. Check out Steve Stuebner's guide: Bookstore
You can buy each section for $.99 as a digital download.
3. 12.5' x 22.5" Sotar Legend. Legends (and their predecessor prototypes) and Wave Destroyers are the cat of choice up there. You don't often see other types of cats.
4. The north fork payette is dam fed from lake cascade. It travels through a valley will a lot of agricultural and cattle operations, picking up a fair amount of cow piss and who-knows-what-else. I constantly spit the water out if I get it in my mouth. It's still fairly clean. It may appear cloudy, but a lot of that is because it's very aerated. 100+ fpm churns the hell out of it. The good thing is that the water is very warm - probably the warmest water I've ever run. The south fork payette is different. It too has a dam fed tributary, but the water from that dam comes from way deep in the reservoir. Cascade lake by comparison is shallow and large and the water warms up considerably there. The south fork is much more clear. Above lowman, the south fork has a glacial teal color to it most of the year. Once the deadwood river enters, it becomes cold and clear until the confluence.